Wed Feb 14 Meteorology for Chicago

[Brett Crapser]

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1125 AM CST Wed Feb 14 2024

KEY MESSAGES...

- Rain moves in tonight through Thursday morning. There is a
chance (30%) for slushy snow to mix in Thursday morning for
counties along the Wisconsin border.

- A chance (30-50%) of snow Friday.

&&

DISCUSSION...
Issued at 241 AM CST Wed Feb 14 2024

Patchy clouds are drifting east as an upper level wave exits
the region. Brief clearing is expected to develop for Wednesday
morning, but increasing high clouds move in during the afternoon
ahead of the next system. Temperatures will once again warm
above 40 for most of the area.

The next upper level wave is on track to pass over Chicago from
Wednesday night through Thursday morning. With plenty of moisture
advecting in from the west-southwest and deep forcing, it looks
likely the area will get its next round of precipitation through the
night. With steep lapse rates aloft, isolated rumbles of thunder
are possible Wednesday night but left the mention of it out of
the forecast for the time being. Latest guidance has once again
shifted the track of the surface low, this time more to the
north. While this would allow for warmer temperatures to support
a mainly rain system, the amount of flip flopping that models
have done with this system over the last four days lowers
confidence. Rain can be expected for locations south of I-88.
But for areas north, particularly along the border with
Wisconsin, the coldest guidance is suggesting near-freezing
surface wet bulbs associated with stronger dynamic cooling and
a more southerly surface low track to support a wet, slushy
snow could mixing in. A sharp gradient between rain and more
appreciable snow accumulations will exist, and as a result, just
a small wobble south would result in an increased threat for
slippery travel conditions for additional areas down to around
I-88.

With prevailing northwest flow, an active pattern will remain
over the area. The next upper level wave moves in as it swings
around the deepening low in northern Ontario on Friday. Models
have shifted the f-gen circulations slightly to the south as
this next wave passes over, which keeps the current forecast
with lighter accumulations. However, with a colder air mass
aloft, there is better confidence in precipitation being all
snow. Behind this system, a colder airmass will move in allowing
surface high temperatures to remain below freezing on Saturday.
Beyond Saturday, ensembles are suggesting weak ridging aloft
which may provide a brief break in the train of weather systems
and return temperatures to seasonal norms.

DK

&&

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1125 AM CST Wed Feb 14 2024

- SHRA late tonight with MVFR VSBY reductions and possible TS

- Brief window for LLWS roughly 07-11z

- MVFR CIGS expected Thursday morning

There are no significant aviation weather concerns through this
evening. Winds remain light out of the SSW becoming SE after
sunset. Winds then gradually veer back to the south and
southwest overnight ahead of an approaching weather system and
increase in speeds. In tandem a southwesterly low-level jet will
begin strengthening to around 50kt at 2000ft just ahead of the
system and could result in a brief period of LLWS prior to the
SE surface winds turning SW and stronger gusts mixing down to
the surface. Due to the short window opted to hold off on a
formal TAF mention though it may be considered with later
updates.

Showers are expected to move in just before midnight (earliest
at RFD) and move across the area through early Thursday morning,
ending around 11-13Z from west to east. There is a window where
convective showers move across the terminals, currently
highlighted in TEMPO groups for 3SM SHRA. A few rumbles of
thunder certainly can`t be ruled out but have left out of the
TAFs for now to to lower confidence and expected lower coverage.
Latest guidance continues to favor mainly rain with this system
though a few snowflakes may try to mix in Saturday along the
WI/IL stateline though this favors remaining north of the
terminals and have kept SN out of the TAFs with this update.

Strong and gusty northwest winds will develop behind the system
with the passage of a cold front, when gusts could approach the
upper 20 to lower 30kt range. CIGS will also remain MVFR
through much of the morning before scattering out late morning
into early afternoon.

Petr

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 3 AM to 6 PM CST Thursday for
Winthrop Harbor IL to Gary IN.

Small Craft Advisory from 3 AM Thursday to 3 AM CST Friday for
Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$